Joining processes for powder metallurgy parts: a review

Abstract

Powder metallurgy (PM) processes have high productivity and are ideal for making near net-shape parts of complex geometries from a range of materials, which maximises material utilisation, and minimises or eliminates secondary operations such as machining. The secondary operations that are common for components made via liquid metal processing may result in additional manufacturing steps with substantial cost and waste implications. Despite this obvious advantage of PM components, including powder metal injection moulded (MIM) parts, the joining of sintered powder materials has been associated with difficulties related to their inherent characteristics, such as porosity, contamination and inclusions, at levels which tend to influence the properties of a welded joint. A critical review of the current state of the art of welding PM components is presented. The intention is to identify preferred joining processes and identify technology gaps in joining of PM parts, in terms of initial processing and attendant materials issues, with an emphasis on offering solutions to welding problems. Brazing, diffusion bonding and shrink fitting are briefly considered in addition to welding.